Switched digital video (SDV) refers to an arrangement in which broadcast channels are only switched onto the network when they are requested by one or more subscribers, thereby allowing system operators to save bandwidth over their distribution network. In conventional cable or satellite broadcast systems, every broadcast channel is always available to all authorized subscribers. In contrast, a switched digital video channel is only available when requested by one or more authorized subscribers. Also, unlike video on-demand, which switches a singlecast interactive program to a user, switched digital video switches broadcast streams, making each stream available to one or more subscribers who simply join the broadcast stream just as they would with normal broadcast services. That is, once a switched service is streamed to a subscriber, subsequent subscribers associated with the same service group as the first subscriber can tune to the same broadcast stream. The switched digital video will often share the same resource managers and underlying resources with other on-demand services.
As noted, switched digital video is largely a tool to save bandwidth. From the subscriber perspective, he or she still receives the same broadcast video service when using a switched broadcast technique; ideally the user is not able to discern that the stream was switched at all. If each one of the digital broadcast channels is being watched by subscribers in the same service group, the switched digital video approach does not yield any bandwidth savings. However, a more likely situation statistically is that only a certain number of the digital broadcast channels are being watched by subscribers in the same service group at any given time. Those channels not requested by a subscriber need not be broadcast, thereby saving bandwidth.
One way to support switched digital video is to utilize a session manager to manage SDV sessions and provision services. The subscriber's receiver (e.g., a set top terminal) will request an SDV program from the session manager. The session manager will determine if the requested channel is already being sent to the corresponding service group that the subscriber belongs to. The subscriber receiver will be assigned to join the existing SDV service if the requested channel is available at the service group or assigned to a new SDV service if the requested channel is not available at the service group. The Session Manager will negotiate with the edge devices to allocate resources required for the service. The edge device (e.g., a digital modulator such as a QAM modulator) needs to dynamically retrieve the MPEG single program transport stream that carries the requested broadcast program (likely via IP unicast or multicast) and generate the MPEG multiple program transport stream. As part of the service setup response message, the video tuning parameters such as frequency and MPEG program number are sent back to the subscriber to access the requested broadcast channel.
When a subscriber is viewing an SDV program it occasionally may be necessary to transfer the program from one edge device to another in order, for example, to balance out the number of programs being supplied by the edge devices. When performing such a transfer, the SDV manager sends a message requesting the set top terminal to tune to a channel corresponding to the program's new frequency and program number using a so-called force tune function or process.
Subscriber receivers such as set top terminals are increasingly incorporating digital video recorder (DVR) functionality to record programming that is received over the content delivery system. DVRs can be used to record SDV and non-SDV (e.g., broadcast) programming. In many cases the subscriber can conveniently record a desired program using an electronic program guide (EPG), which is an interactive, on-screen display feature that displays information analogous to TV listings found in local newspapers or other print media. An EPG provides information about each program being broadcast within the time period covered by the EPG, which typically ranges from the next hour up to several days. The information contained in an EPG includes programming characteristics such as, for example, channel number, program title, start time, end time, elapsed time, time remaining, and a brief description of the program's content. Using the DVR system, the EPG allows the viewer to automatically record a program based on the information in the EPG.
If a force tune process is initiated while a subscriber is recording an SDV program using the DVR functionality available on the set top terminal, the recording process will generally terminate. Thus, the subscriber will only record the portion of the program that was received before the force tune occurred. In order to record the remaining portion of the program, the subscriber would need to manually re-start the recording process using the new tuning information available through the EPG. Not only is this disruptive and inconvenient for the subscriber, it also results in the creation of two separate recording files—one for the part of the program that was recorded before the force tune and one for the part of the program that was recorded after the force tune. The subscriber would thus need to play back two files in order to view the entire SDV program, which is a further inconvenience for the subscriber.
Accordingly, it would be desirable to provide a method and apparatus that allows an SDV program to be recorded in a manner that is least disruptive to the subscriber when a force tune occurs. That is, the recording process should require no subscriber intervention during both recording and playback and should minimize any discernable disruption within the recorded program itself